Deck Screws, Flush or Countersink, That is the Question?


Finally, the second-best part of building a deck, screwing down the deck boards. Attaching the decking to the joists with face screws but wait! Should face deck screws be flush with the decking or countersunk below the decking surface?

Deck screws should be slightly countersunk below the decking surface. The finish screws set to approximately 1/8″ (3mm) below the decking’s surface. Providing a clean finish without any screw head protruding after the decking dries.

The biggest concern is snagging your socks on a screw as you stroll across the deck. Ouch, if you are going to do that, you misewell pound nails in your decking and go into the house and cry!

All drama aside. The goal when setting deck screws is for a clean finish. Running your hand over the decking without catching slivers or screw heads. This is why screw heads need to be set slightly below the surface. Then when the decking shrinks, and it will, the screw’s head will still be below the surface.

Regardless of how dry the decking comes from the mill, it will always shrink. Wood decking shrinks and expands roughly 3% from summer to winter. Meaning 5/4″ wood decking, being 1″ (25mm) thick, will shrink around 1/32″ (1mm) from summer to winter. Countersinking the screw a 1/8″ (3mm) ensures that there is no chance the screw head will protrude above the decking.

This also happens after you install the decking. I often install wood decking tight even though it needs gapping for proper drainage and ventilation. For I know by the end of the summer, the decking will have dried out, leaving a 3/16″ to ¼” gap between boardsOpens in a new tab.. The perfect gapping between deck boards.

The same preplanning needs to be done with setting deck screws. If you set the deck screws flush with the decking. When the decking shrinks, the screws head will all set proud of the decking. Making an extremely uncomfortable deck to walk on.

Setting Deck Screws Flush Draws Attention to the Screws

Aesthetically, deck screws set flush to the decking draw attention to the wrong part of the deck. The star of the deck is the decking, not the screws. The screws are to be that behind the scenes hero that makes the star shine. No one ever says

“Come outside and take a look at my screws.”

No, it’s the deck and the decking to be admired. Screws are only there to holding the decking in place. Setting them slightly below the decking surface. Makes the screws

“out of sight, out of mind.”

Which is what you want. You know when you are driving through Saskatchewan with nothing but flat prairies, a beautiful open expanse, just like your decking. But you see every little hill or rock protruding out of the flat prairie, but you haven’t noticed the thousand gopher holes you passed. The same with decking screws. Protruding will be seen, along with flush, but slightly countersunk below the surface, you will notice nothing.

Installing Deck Screws in Decking

Along with setting the screws slightly below the surface, a few good practises help screws do their job without drawing attention to them.

With a 5 ½” decking board, every joist should be screwed with two screws set 1″ (25mm) from the edge of the decking, in a straight line. Creating a consistent pattern on the decking.

Roughly 350 screws for every 100 square feet of decking.

To aid in installing the screws in a straight line, you can snap a chalk line on the decking on at the center of each joist. You can use the ruler on your rafter square to measure the distance from the edge for each screw for the first few boards. After you get the hang of it, you can eyeball it. If you have fat fingers like me, an inch is roughly the width of my fat knuckle on my pointer finger. Just a quick guide if you need a reference while screwing the decking.

Deck Screws Are Designed to be Countersunk

All quality deck screws have a bugle head and smooth shank below the head. This is for the screw can be countersunk, and the wood can push pass the head when it swells. The very design of a deck screw cries to be countersunk, not flush to the decking.

Will Countersinking Deck Screws Pool Water?

Yes, the slight dimple of the screws set below the decking surface will initially pool water. Increasing rot and collecting dirt, or so the argument goes.

This may be a more significant concern for hardwood decking, which has less movement and is harder. But with pressure treated decking, the softwood will actually heal over the dimple mark. No, not like some crazy scene from X-men, but as the rain pours over the decking, the wood will swell, closing in the hole around the screws. To the point where you will not notice many of them.

Second, unless you are in an extremely wet environment, the amount of water collecting in the decking dimple is minor and will quickly evaporate once the sun comes out. We are talking, not even a millimetre of water around each screw head. A bigger issue is decking cupping collecting water then screw heads.

Edge Screwing is Even Better Than Face Screwing Decking

An even better solution to countersinking screws is edge screwing decking. Big fan of the Camo edge screw system. With their self-drilling screws, fasten on the edge of the decking. Removing ugly water pooling screw heads from the surface of the decking. At the same time, holding the decking exactly where it needs to be held, the edge of the board. Camo tool also has the advantage of a built-in spacer. Gapping the decking boards consistently with every screw.

Maybe a better question than “should deck screws be flush” is, “should decking be edge screwed?”. Yes, yes, it should. Edge screwing is the better way to attach decking. Proving a cleaner decking surface with increase holding power minimizing decking cupping.

If you are ready for a beautiful deck without ugly screw heads marring the surface.

Conclusion: Deck Screws Should Be Counter Sunk Never Flush

Installing deck screws slightly below the surface accommodate the shrinking of the decking as the boards dry. Doing this will create a clean surface for the decking for walking on while minimizing the visual effect of the screw heads.

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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